Barnes & Noble (BKS-0.8%) announces the Nook HD and Nook HD+ are available for preorder online. The consensus on the Street is that the new Nook products keep Barnes & Noble in the game, but that finding room for margins is going to be quite tricky. Prices for the new Nook products are set below the expected prices for Apple's soon-to-be-unveiled smaller iPad, but in a tight range with other rival products.